smitley



Jan. 24, 1956 Filed Aug. 4, 1953 M. L. SMITLEY 2,732,191

DUAL CARBURETOR 2 Sheets-Sheet 1 ooe-olo'LEnx smxsn INTO 55m 46 )QY 17MX Marion 1/. Sm iil y' IN VEN TOR.

Jan. 24, 1956 M. L. SMITLEY 2,732,191

DUAL CARBURETOR Filed Aug. 4, 1953 2 Sheets-Sheet 2 Fig: 2

Maria)? L. Smiil 0 7 IN VEN TOR.

BY M,

United States Patent F DUAL CARBURETOR Application August 4, 1953,Serial No. 372,325

1 Claim. (Cl. 261-23) The object of this invention is to improve theoperation of a two-stage carburetor. Carburetors of the progressive typehave been known for fifty years (e. g. Bollee #871,320; Lancia1,180,483; Friz 1,449,664; Ball & Ball of 1916 and the 1941 Buick).However, for these fifty years no one has ever produced an entirelysatisfactory two-stage carburetor and each attempt, after a brief life,has been abandoned. Y

The transition from the first to the second stage has not beensufliciently smooth to be accepted by the public.

The object of this invention is, therefore, to improve this transitionand satisfy the public.

Figure 1 shows diagrammatically the preferred form of my invention.

Figure 2 shows an actual reduction to practice on the exact lines laiddown in Figure 1.

In Figure l:

is the air entrance of the venturi 12 and into which discharges a fuelnozzle 14. The venturi is controlled by a choke valve 16 as shown inPatent #2,547,873, located in the throat of the venturi 12 so that thenozzle is always under suction in all positions of the choke 16.

18 is the throttle which controls the discharge of air and fuel to theengine from the primary carburetor.

28 is the second throttle for the secondary carburetor.

20 is the primary throttle lever which is manually controlled.

21 and 23 are the two primary low speed fuel. outlets that insure asmooth transfer from idle to low speed operation.

22 is the throttle link which insures that the secondary throttle 28 isclosed whenever the primary throttle 18 is closed, but permits thesecondary throttle 28 to remain closed after 18 is opened.

24 is a slot in the lever 26 which controls the secondary throttle 28 topermit this one-way control of the secondary throttle 28.

30 is the secondary venturi into which the secondary fuel nozzle 32discharges.

34 is the eccentrically controlled throttle shaft for the secondarythrottle 28.

The eccentricity of this throttle shaft 34 is 0.055 inch on thedownstream side of the inclined throttle 28. This insures that enginesuction when the throttle 18 is closed will positively close thesecondary throttle 28 and will overcome any friction which otherwisewould allow an air leakage to disturb idling.

The secondary throttle lever 26 is connected by a link 36 with thediaphragm 38 which forms the right hand wall of the diaphragm suctionchamber 40. The suction chamber 40 is maintained at subatmosphericpressure by means of the pipe 42 which is in restricted communicationwith the venturi 12 of the primary carburetor in all positions of thechoke valve 16 at the opening 44.

Check valve 46 is supported by the spring 48 located in the body 43 ofthe chamber 50.

This check valve 46 is not exactly tight on its seat. A leak having adimension of around 7 or 8 thousandths of P I Cc I 2,732,191

Pa terned Jan. 24, 1956 an inch in diameter is put into the seat so thatwhen the valve is seated, suction will slowly build up in the chamber40. r

The spring 50 is provided to normally keep the secondary throttle 28closed and to permit the secondary throttle to open slowly under theinfluence of suction in the venturi 12 but to permit the throttle 28 toclose promptly when entering on a hill and slowing down.

In Figure 2:

Similar parts having similar numbers; for example, 116 is the chokevalve in the primary carburetor located in the primary venturi 112. 114is the nozzle for the primary venturi. 118 is the throttle to theprimary carburetor. 115 is a passage for air and fuel from the floatchamher 117 (see Patent #2,547,873 referred to above).

132 is the nozzle for air and fuel for the secondary carburetordischarging into the secondary venturi 130.

126 is the slotted throttle lever for the secondary throttle 128.

124 is the slot in lever 126.

As before, the throttle 128 is 0.055 inch off center and its diameter is1%(;''.

136 is the rod connecting diaphragm 138 (which has a diameter of 1%")with the lever 127 which is rigidly mounted on the throttle shaft 129 asis the slotted lever 126. 1

A loose link 131 connects in the slot 124 with the primary throttlelever so that if primary throttle 118 is closed, then secondary throttle128 will also be closed; but the throttle 118 can be opened and thesecondary throttle 128 will remain closed.

A spring 150 located in the chamber 140 tends to keep secondary throttle128 closed.

A spring 148 tends to seat the ball check valve 146 against a seat 147which is provided with a leak so that the pressure in chamber-140 canfall only slowly, but can rise rapidly.

b 121, 123, 125, 127 are four low speed outlets controlled y 11ga Theposition of the upstream lip of the throttle (b) The lowest orifice 127is controlled by the low speed idling control valve 129.

This is the low speed control system.

A passage 142 connects the left hand side of check valve 146 through theleak with the restriction 144 in throat 112.

Operation As before, if the load is reduced, as when running downhill,then all the power needed is derived from the primary carburetor and thesecondary throttle 128 remains closed. Again, if the throttle 118 iswide open as when climbing a hill, then the suction in the primaryventuri 112 is too low to overcome the spring 150. The throttle 128still remains closed by the pressure exerted by the spring 150. Now, ifthe flow through venturi 112 exceeds a safe top limit, suction at 144 inthe throat is transmitted through the pipe 142 past the leak around thecheck valve 146 to the chamber 140. The pressure in chamber 140 slowlyfalls and eventually, the throttle 128 opens. If the throttle 118 issuddenly closed, the link 131 engages the left hand end of slot 124 andthe secondary throttle 128 is positively closed. The spring 148 isselected so as to permit the ball valve 146 to move easily to the leftso that the diaphragm 138 can also easily move to the right.

What I claim is:

In a two stage carburetor having a primary and a secondary venturi,mixing chambers and two mixture outlets in parallel, two butterflythrottles, one in each outlet, means for positively opening the throttlecontrolling the primary mixture outlet; said secondary throttle beingoftset so that the upstream lip is longer than the downstream lip byapproximately ".where the throttle has a diameter of about 1.31 inchesso as to be held closed by inlet manifold suction, a oneway lost motionconnectionfromthe primary to said secondary throttle so that the primarythrottle positively closes said secondary throttle when the primarythrotde is closed, a chamber, a moving wall therein positively connectedto said secondary'throttle lever, a passage from said chamber to thethroat of the primary venturi of said primary mixing chamber, a checkvalve therein, a valve seat thencfor, a light spring pushing said valveon said seat and a restricted by pass around said valve to admit airfreely to said chamber when said secondary throttle is positively closedand to delay the automatic opening of said secondary throttle by delay:ing the admission of low pressure air to said chamber through saidrestricted by pass, said moving wall being responsive to the suctionadmitted past said check valve to said chamber and positively connectedto the secondary throttle.

References Citedinthe file of this patent UNiTED STATES PATENTS2,376,732 Strebinger May 22, 1945 2,609,807 Winkler Sept. 9, 19522,647,502 Braun Aug. 4, 1953

